1. Field of the Invention
The present invention relates to a trap apparatus for use in an evacuating system for evacuating a vacuum chamber for a semiconductor fabrication apparatus or the like.
2. Description of the Related Art
A conventional evacuating system will be described below with reference to FIG. 7. In FIG. 7, a hermetically sealed chamber 10 comprises a process chamber for use in a semiconductor fabrication process such as an etching apparatus or a chemical vapor deposition (CVD) apparatus. The hermetically sealed chamber 10 is connected to a vacuum pump 12 through a discharge path 14. The vacuum pump 12 serves to increase the pressure of gases discharged from the process in the hermetically sealed chamber 10 to an atmospheric pressure. An oil-sealed rotary vacuum pump has heretofore been used as the vacuum pump. A dry pump is mainly used as the vacuum pump at present.
If the degree of vacuum required by the hermetically sealed chamber 10 is higher than the ultimate vacuum of the vacuum pump 12, then an ultra-high vacuum pump such as a turbo-molecular pump is additionally disposed upstream of the vacuum pump 12.
Gases discharged from some processes are toxic and/or explosive depending on the type of the process, and hence cannot be directly released into the atmosphere. Therefore, a discharged gas treatment apparatus 16 is provided downstream of the vacuum pump 12.
Among gases, discharged from the process, whose pressures are increased to an atmospheric pressure, gas components that cannot directly be discharged into the atmosphere are treated by a process such as adsorption, decomposition, or absorption. Only harmless gases are discharged from the discharged gas treatment apparatus 16 into the atmosphere. Necessary valves are provided at appropriate locations of the discharge path 14.
The conventional evacuating system has the following disadvantages.
In the conventional evacuating system, if reaction by-products contain a substance having a high sublimation temperature, then the gas of the substance is solidified while its pressure is being increased, and deposited in the vacuum pump 12. This tends to cause a failure of the vacuum pump.
For example, when BCl3 or Cl2 which is a typical process gas for aluminum etching is used, the remainder of the process gas of BCl3 or Cl2 and a reaction by-product of AlCl3 are discharged from the hermetically sealed chamber 10 by the vacuum pump 12. AlCl3 is not deposited at the suction side of the vacuum pump 12 because its partial pressure is low. However, while AlCl3 is being discharged under pressure, its partial pressure rises to cause AlCl3 to be deposited, solidified and attached to the inner wall of the vacuum pump 12, resulting in a failure of the vacuum pump 12. The same problem occurs with reaction by-products such as (NH4)2SiF6 and NH4Cl that are produced in a CVD apparatus for depositing films of SiN.
It has heretofore been attempted to heat the vacuum pump wholly to pass the reaction by-products in gaseous state through the vacuum pump so that no solid substance is deposited in the vacuum pump. This attempt has been effective to prevent a solid substance from being deposited in the vacuum pump. However, it has been problematic in that a solid substance is deposited in the discharged gas treatment apparatus disposed downstream of the vacuum pump, thereby clogging a filled layer in the discharged gas treatment apparatus.
Therefore, it is conceivable that a suitable trap apparatus such as a low-temperature trap is provided upstream of the vacuum pump to trap components which are liable to solidify and are contained in the discharged gas. In this case, the trap apparatus is required to prevent most components contained in the discharged gas from passing therethrough without being deposited in a trap unit, thereby improving the trap efficiency and thus enhancing the reliability thereof.
Further, since trapped solids are accumulated on the trap unit of the trap apparatus, after the elapse of a certain period of time, the replacement of the trap unit or the removal of the solids by a predetermined method to regenerate the trap unit is required. In the former, a large number of trap units should be provided, and it is difficult to automate the operation of the system. An example of a possible method for realizing automatic operation is to provide a regeneration chamber adjacent to the trap chamber. In this method, the trap unit is positioned within the regeneration chamber, and, in this state, a regeneration liquid, such as hot water or a chemical liquid, heated to a predetermined temperature is allowed to flow through the regeneration chamber to regenerate (clean) the trap unit, thus making it possible to perform automatic operation. In this case, it is required to improve regeneration efficiency and enhance the reliability of the trap apparatus.
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a trap apparatus which can improve its reliability by virtue of the improved efficiency of trapping products, or the improved regeneration efficiency, i.e., the improved efficiency of removing products deposited on the trap unit to regenerate the trap unit.
In order to achieve the above object, according to one aspect of the present invention, there is provided a trap apparatus disposed in a discharge path for evacuating a hermetically sealed chamber through a vacuum pump, the trap apparatus comprising: a trap unit for depositing thereon a product contained in a discharged gas and removing the product, the trap unit having a surface which has been subjected to hydrophilization treatment.
The hydrophilization of the trap unit on its surface makes the surface energy smaller than the condensation force of a liquid. By virtue of this treatment, even a product, which is difficult to be trapped, is likely to be adsorbed on the surfaces of baffle plates, thus improving the trap efficiency. Examples of hydrophilization treatment include fluorocoating with hydrophilic ions incorporated therein.
According to another aspect of the present invention, there is provided a trap apparatus comprising: a trap chamber disposed in a discharge path for evacuating a hermetically sealed chamber through a vacuum pump, the trap chamber housing a trap unit for depositing thereon a product contained in a discharge gas and removing the product; a regeneration chamber disposed adjacent to the trap chamber for introducing a regeneration liquid to regenerate the trap unit; and a switching mechanism for switching the trap unit between the trap chamber and the regeneration chamber, the trap unit having a surface which has been subjected to water repellent treatment.
The water repellent treatment of the trap unit on its surface suppresses the surface energy, and can facilitate the condensation of a liquid. This prevents spreading of the liquid on the surfaces of the trap unit, and can easily repel the liquid. Therefore, even if baffle plates having a complicated shape are used to improve the trap efficiency in the trap unit, when the baffle plates are regenerated with a regeneration liquid, the regeneration liquid can be easily repelled from the surfaces of the baffle plates. This can improve the efficiency of washing and drying, i.e., the regeneration efficiency, and consequently can improve the operating efficiency, and thus the trap efficiency. An example of water repellent treatment is coating of a fluororesin such as tetrafluoroethylene polymer.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.